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/*:
 
 #20 Valid Parentheses
 
 Given a string containing just the characters `'('`, `')'`, `'{'`, `'}'`, `'[' ` and `']'`, determine if the input string is valid.
 
 An input string is valid if:
 
 1. Open brackets must be closed by the same type of brackets.
 2, Open brackets must be closed in the correct order.
 
 Note that an empty string is also considered valid.
 
 Example 1:
 ```
 Input: "()"
 Output: true
 ```
 
 Example 2:
 ```
 Input: "()[]{}"
 Output: true
 ```
 
 Example 3:
 ```
 Input: "(]"
 Output: false
 ```
 
 Example 4:
 ```
 Input: "([)]"
 Output: false
 ```
 
 Example 5:
 ```
 Input: "{[]}"
 Output: true
 ```
 
 */
import Foundation

class Solution {
    // 使用栈解决
    func isValid(_ s: String) -> Bool {
        var stack: [Character] = []
        
        for c in s {
            if c == ")" {
                if !stack.contains("(") {
                    return false
                }
                stack.popLast()
            } else if c == "]" {
                if !stack.contains("[") {
                    return false
                }
                stack.popLast()
            } else if c == "}" {
                if !stack.contains("{") {
                    return false
                }
                stack.popLast()
            } else {
                stack.append(c)
            }
        }
        
        return stack.isEmpty
    }
}

print(Solution().isValid("()"))
print(Solution().isValid("()[]{}"))
print(Solution().isValid("(]"))
print(Solution().isValid("([)]"))
print(Solution().isValid("{[]}"))

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